Interestingly, it is difficult (or even impossible) to port in a 2D CAD drawing to use as the basis of a 3D CAD drawing. Scott
Boy, is that a true statement. I'm a long way from being an expert in this, but I've found you need to plan how you intend to machine the part as you are drawing it. For most things, a 2D drawing is all you need. You can layer the drawing to give depth to the machined part, but you have to plan how the cutting is going to go as you are doing the drawing.
The 3D drawings, Rhino include requires you to develop a surface that can be machined.
A drawing done for Meshcam, just won't work for Sheetcam and the reverse it true. If you are going to cut ply and balsa parts, then you what a 2D drawing to work with. If you are going to machine, say the face of a pilot for your model, then a full 3D drawing is going to be required.
Another point on 3D machining. Full function 4 axis CAM software is going to be very expensive. Programs such as Meshcam take the approach of indexed 2 1/2D machining. This is quite different than a coordinated four axis move.
There is one package. CNCToolkit that does generate coordinated four, and five axis moves. You can find it on Yahooo Groups. I followed it for a while, but the CAD software, although free was difficult to use, at least for my 2D mindset. The work it produces is impressive though.
The issue is, "will your CAD and CAM software generate coordinated four axis moves.And do your really need that for what you are going to cut.